Co-combustion of municipal solid waste and coal gangue in a circulating fluidized bed combustor

Mixed incineration of municipal solid waste (MSW) in existing coal gangue power plant is a potentially highefficiency and low-cost MSW disposal way. In this paper, the co-combustion and pollutants emission characteristic of MSW and coal gangue was investigated in a circulating fluidized bed (CFB) combustor. The effect of MSW blend ratio, bed temperature and excess air ratio was detailedly studied. The results show the NOX and HC1 emission increases with the increasing MSW blend ratio and the SO2 emission decreases. With the increase of bed temperature, the CO emission decreases while the NOX and SO2 emission increases. The HC1 emission is nearly stable in the temperature range of 850-950℃. The increase of excess air ratio gradually increases the NOX emission but has no significant effect on the SO2 emission. The HC1 emission firstly increases and then decreases with the increase of excess air ratio. For a typical CFB operating condition with excess air ratio of 1.4, bed temperature of 900℃ and MSW blend ratio of 10%, the original CO, NOX, SO2 and HC1 emissions are 52, 181, 3373 and 58 mg/Nm^3 respectively.

Study on Co-combustion Characteristics of Superfine Coal with Conventional Size Coal in O₂/CO₂Atmosphere

The pulverized coal combustion in O2/CO2 atmosphere is one of the promising new technologies which can reduce the emission of carbon dioxide and NOx. In this study, the combustion behaviors of different mixing ratio of Shenhua coal with 20 μm and 74 μm particle size in the O2/CO2 atmosphere and air atmosphere were studied by using a thermal-gravimetric analyzer. The combustion characteristics such as ignition and burnout behavior were investigated in the temperature from 20℃ to 850℃. The influence of mixing ratio on combustion characteristics was conduced. The results obtained showed that the ignition temperature of the two kinds of particle size in O2/CO2 atmosphere is higher than in the air, while the activation energy in O2/CO2 atmosphere is lower. With the increasing ratio of 20 μm superfine pulverized coals, the ignition temperature and the activation energy decreased, while the DTG peak value increased, the maximum burning rate position advanced. There were three trends for the ignition temperature curve with the increasing of superfine coal ratio: the ignition of the mixed coal decreased rapidly, then changed less, at last reduced quickly.

Catalytic co-combustion of biomass and brown coal in a fluidized bed:Economic and environmental benefits

The work is devoted to the study of combustion of brown coal,pine sawdust,and their mixtures in a fluidized bed of catalyst at 600-750℃.It is shown that an increase in the content of sawdust in a mixture with brown coal leads to an increase in the burnout degree of solid fuel from 94.4%to 99.9%,while the emission of greenhouse gases in the form of CO_(2)CO and NOxis reduced(CO_(2)from the biomass is not included in the balance).The high content of alkaline earth metal oxides(CaO and MgO)in the mineral part of brown coal,sawdust,and their mixtures eliminates the emission of sulfur oxides and the slagging of heat-exchange surfaces during the combustion in a fluidized bed of catalyst.The optimal temperature,when the highest burnout degree of the above fuels is achieved in the combustion is 750℃.It is also shown that the increase in temperature and the content of sawdust in the composition of the fuel mixtures has a positive effect on the economic and environmental process indicators.

Numerical simulation on optimization of structure and operating parameters of a novel lean coal decoupling burner

Due to its low volatile characteristics of lean coal,it is difficult to catch fire and burn out.Therefore,high temperature is needed to maintain combustion efficiency,while,this leads to high nitrogen oxide emission.For power plant boilers burning lean coal,stable combustion with lower nitrogen oxide emission is a challenging task.This study applied the 3D numerical simulation on the analysis of a novel de-coupling burner for low-volatile coal and its structure and operation parameters optimization.Results indicate that although it was more difficult for lean coal decoupling burner to ignite lean coal than high volatile coal,the burner formed a stepwise ignition trend,which promoted the rapid ignition of lean coal.Comparison of three central partition plate structure shows that in terms of characteristics of the flow field distribution,rich and lean separation and combustion,the structure with an inclination of 0°showed good performance,with its rich-lean air ratio being 0.85 and concentration ratio being 22.94,and there was an apparent decoupling combustion characteristic.Finally,the structure of the selected burner was optimized for its operational conditions.The optimal operating parameters was determined as the primary air velocity of 24.9 m·s^-1 and the mass flow rate of pulverized coal of 2.5 kg·s^-1,in which the pyrolysis products were utilized as reductive agent more fully.Eventually,the nitrogen oxide was efficiently reduced to nitrogen,which emission concentration was 61.88%lower than that in the design condition.

Combustion characteristics and synergy behaviors of biomass and coal blending in oxy-fuel conditions: A single particle co-combustion method

Co-combustion biomass and coal can effectively reduce the emission of CO_2. O_2/H_2O combustion is regarded as the next generation of oxy-fuel combustion technology. By co-combustion biomass and coal under oxy-fuel condition, the emission of CO_2 can be minimized. This work investigates the co-combustion characteristics of single particles from pine sawdust(PS) and bituminous coal(BC) in O_2/N2, O_2/CO_2 and O_2/H_2O atmospheres at different O_2 mole fractions(21%, 30% and 40%). The experiments were carried out in a drop tube furnace(DTF), and a high speed camera was used to record the combustion process of fuel particles. The combustion temperature was measured by a two-color method. The experiments in O_2/N2 atmosphere indicate that the particles from pine sawdust and bituminous coal all ignite homogeneously. After replacing H_2O for N2, the combustion temperature of volatiles of blended fuel particles decreases, while the combustion temperature of char increases. The ignition delay time in O_2/H_2O atmosphere is shorter than that in O_2/N2 or O_2/CO_2 atmosphere. The combustion temperature of volatiles of blended fuel particles increases as the mass fraction of bituminous coal increases, while the combustion temperature of char of blended fuel particles is higher than that of biomass or bituminous coal. The ignition delay time of blended fuel particles increases with the increasing mass fraction of bituminous coal, and the experimental ignition delay time of blend fuel particles is shorter than the theoretical one. These reveal a synergy during co-combustion process of pine sawdust and bituminous coal.

Combustion Characteristics and NO Emissions during Co-Combustion of Coal Gangue and Coal Slime in O_(2)/CO_(2) Atmospheres

Coal slime has low ash content,and adding coal slime during coal gangue combustion may have influence on combustion character;and at this process,NO will emit,and lead to environmental pollution.O_(2)/CO_(2)atmosphere is conducive to NO emission reduction.Thus combustion characteristics and NO emissions during co-combustion of coal gangue and coal slime in O_(2)/CO_(2)atmospheres were studied.The results showed the addition of coal slime increased the combustion activity of the mixed fuels in both air and O_(2)/CO_(2)atmospheres.During co-combustion,there are synergistic effects between them at the fixed carbon combustion stage,and higher blending ratio of coal slime leads to stronger synergistic effect.Furthermore,this study also showed that with the increasing of coal slime blending ratio,the emission concentration of NO increases gradually;with the increase of temperature and O_(2)concentration,the NO emission concentration also gradually increases,and higher O_(2)concentration leads to shorter time required for the complete release of NO.Besides that,the results also demonstrate that the proportion of pyrrole and nitrogen oxide in the ashes increases with the increase of combustion temperature,and pyridine and quaternary nitrogen gradually disappear,while the total nitrogen content in ash decreases with the increase of temperature.The results will contribute to a better understanding of the co-combustion process of coal gangue and coal slime in O_(2)/CO_(2)atmosphere,and provide basic data for the practical industrial application of coal gangue and slime.

Heavy Metal Migration Characteristics of Co-Combustion between Sewage Sludge and High Alkaline Coal on Circulating Fluidized Bed

The migration characteristics of heavy metals in co-combustion of sewage sludge and high alkali coal in circulating fluidized bed were studied by experiments and simulations. Temperature plays a crucial role in thermodynamic equilibrium distribution and migration characteristics of heavy metals. At the temperature range of 700℃-1200℃, Hg is completely gaseous and the proportion of Pb, Ni, and Cd in the gas phase is also high. As is mainly elemental in the system, and the proportion of Cr in the solid phase is large. Zn compounds are diverse and mostly solid materials. The volatility of Cu is not strong, and it will become gaseous when the temperature exceeds 1700℃. The proportion of heavy metals in the gas phase decreases as the excess air ratio increases. In an oxygen-rich atmosphere, most of Zn and Ni are converted to oxides;Pb and Cd are converted to crystalline silicate;Cu is converted to partial aluminate;Cr compound is decomposed to form Cr_(2)O_(3);they are good for the solidification and controlling of heavy metals. The elemental Hg is converted to HgCl_(2) and the elemental As is converted to AsCl_(3). Temperature also has a great influence on the volatilization rate of heavy metals. The higher the temperature, the shorter the time they reach the maximum volatility.

Techno-economic analysis on oxy-fuel based steam turbine power system using municipal solid waste and coals with ultrasonicator sulfur removal

Municipal solid waste(MSW)is a carbon–neutral energy source and possesses a moderate heating value;hence,it can be used as an alternative fuel for coal.To use high ash and high sulfur Indian coals efficiently,a techno economic analysis is performed for electricity generation using supercritical and subcritical based steam turbines operating in the oxy-fuel co-combustion mode of MSW with Indian coals.The impact of the capture of direct and indirect greenhouse gasses such as CO_(2),NO_(x)and SO_(x)on the net thermal efficiency of the power plants is assessed.The supercritical based steam turbine achieved a higher net thermal efficiency by 8.8%using MSW based feedstock compared to sub-critical conditions.The co-combustion mode reduced the levelized cost of electricity(LCOE)by 48–73$/MWh.Techno-economic analysis for sulfur removal in coal using ultrasonication technology has not yet been reported in the literature.The incorporation of an ultrasonicator(a pre-combustion sulfur remover)and a duct sorbent injector(a post-combustion SO_(x)absorber)increased the LCOE by 1.39–2.75$/MWh.In high sulfur coals,the SO_(x)emissions decreased from 224.79 mg/m^(3)to 9.2 mg/m^(3).